A conventional X-ray CT system detects X-rays emitted from an X-ray tube and transmitted through the subject, and reconstruct images based on detection results to obtain an X-ray tomographic image. In the X-ray CT system, the X-ray tube is provided inside an annular rotating body, whose center is a through-opening, into which a bed with the subject can be inserted. The annular rotating body is circumferentially shielded with a cover, which comprises a tubular case part for shielding the annular rotating body, the cover extending from the central side of the opening. Moreover, the tubular case part is provided with an X-ray transmission opening, where X-rays from the X-ray tube pass through.
The X-ray transmission opening is, however, closed with a sheet member for the purpose of ensuring safety. The sheet member prevents the subject from coming into contact with the annular rotating body, and it also protects the interior of the annular rotating body against penetration of blood or contrast agents. Furthermore, the sheet member prevents noise from coming out of the inside of the cover. The noise inside the cover includes a wind noise caused by the rotation of the annular rotating body and the sound of the motor driving it.
The sheet member comprises a thin film-like material having a high transmittance for X-rays and a laser beam that is used for marking the subject. This can suppress deterioration in the quality of images acquired by radiography.
As another type of medical diagnostic apparatus, for example, an MRI system, is provided with a sound absorption material that is applied as a lining to the internal surface of the cover. The silencing effect of the material reduces the noise leaking out of the machine see Japanese Laid-Open Patent Publication No. H8-257008)